Method and apparatus for improving the effects of color burst modifications to a video signal

ABSTRACT

In the known color stripe process for preventing recording of video signals, the color burst present on each line of active video is modified so that any subsequent video tape recording of the video signal shows variations in the color fidelity that appear as undesirable bands or stripes of color error. This color stripe process is improved by a combination of modifying the phase of the color burst on only part of the color burst. Additional improvements were obtained by incorporating techniques of widening the normal color burst envelope towards the trailing edge of horizontal sync and towards the beginning of active video. These techniques are useful in improving the performance of the color stripe process in both the NTSC and PAL color systems. However, additional improvements are described in the PAL system whereby the phase modifications are controlled so as to avoid disturbing the so-called PAL ID pulse. Such avoidance of the PAL ID pulse improves the playability of the color stripe signal in the PAL format.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application, of Ser. No.08/897,132 filed Jul. 18, 1997, now U.S. Pat. No. 5,784,523 which is acontinuation of Ser. No. 08/438,155, filed May 9, 1995 now abandonedentitled METHOD AND APPARATUS FOR DEFEATING EFFECTS OF COLOR BURSTMODIFICATIONS TO A VIDEO SIGNAL BY Ronald Quan and John O. Ryan.

This application claims the benefit of U.S. Provisional ApplicationNumbers: Ser. No. 60/010015, entitled AN IMPROVED METHOD AND APPARATUSFOR MODIFYING THE COLOR BURST TO PROHIBIT VIDEOTAPE RECORDING by WilliamJ. Wrobleski; filed Jan. 16, 1996; Ser. No. 60/010,779 entitled ANADVANCED COLOR BURST AND APPARATUS FOR MODIFYING THE COLOR BURST TOPROHIBIT VIDEO TAPE RECORDING by William J. Wrobleski., filed Jan. 29,1996; Ser. No. 60/014,246 entitled A SYSTEM AND METHOD FOR COPYPROTECTION OF VIDEO RECORDING USING AN ADVANCED AND SPLIT COLOR BURSTSYSTEM by William J. Wrobleski filed Mar. 26, 1996; Ser. No. 60/024,393,entitled METHOD OF COPY PROTECTION OF A PAL COLOR VIDEO SIGNAL byWilliam J. Wrobleski filed Jun. 28, 1996; and Ser. No. 60/021,645entitled METHOD OF IMPROVED COPY PROTECTION OF A PAL COLOR VIDEO SIGNALby William J. Wrobleski filed Jul. 12, 1996. All of the above co-pendingapplications are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Filed of the Invention

The present invention pertains to a method and apparatus for processinga video signal, and more particularly to improving the effects of phasemodulation of the color burst component of the video signal for videocopy protection).

2. Description of the Prior Art

Various copy protection techniques have been developed to modify a videosignal so as to prevent copying or reduce the entertainment value of acopied videocassette (effectiveness) while the same signal produces adisplay on a television receiver or monitor with a minimum of or novisible artifacts.

Video copy protection is defined as a system whereby a copy protectedvideo signal is viewable with a minimum of or no visible artifactswhereby the playback of a recording of such a signal is not possible orproduces a signal that has significantly degraded entertainment value.Copy protection is to be differentiated from video scrambling. Videoscrambling means that the video signal is not viewable. A scrambledsignal may be recordable, but unless it has been descrambled, theplayback of such a recording is still unviewable.

A well known copy protection scheme for video signals include is thatdisclosed in U.S. Pat. No. 4,631,603 ('603), by John O. Ryan, issued onDec. 23, 1986 and assigned to Macrovision, incorporated by reference.The '603 patent is directed to modifying an analog video signal toinhibit making of acceptable video recordings therefrom. This disclosesadding a plurality of pulse pairs to the otherwise unused lines of avideo signal vertical blanking interval, each pulse pair being anegative-going pulse followed closely by a positive-going pulse. Theeffect is to confuse AGC (automatic gain control circuitry) of a VCR(video cassette recorder) recording such a signal, so that the recordedsignal is unviewable due to the presence of an excessively dark picturewhen the recorded signal is played back.

Another well known copy protection is that disclosed in U.S. Pat. No.4,577,216 ('216), “Method and Apparatus For Processing a Video Signal,”John O. Ryan, issued Mar. 18, 1986 and incorporated by reference,discloses modifying a color video signal to inhibit the making ofacceptable video recordings thereof. A conventional television receiverproduces a normal color picture from the modified signal. However, theresultant color picture from a subsequent video tape recording showsvariations in the color fidelity that appear as bands or stripes ofcolor error. Colloquially the modifications are called the “Colorstripe™system” or the “Colorstripe™ process”. Commercial embodiments of theteachings of this patent have typically limited the number of videolines per field having the induced color error or color stripes.

The teachings of the '603 patent are useable in analog video cassetteduplication and various digital transmission and recorder playbacksystem such as DVD, DVCR and satellite services utilizing a digital settop decoder. The teachings of the '603 patent depend upon the actions ofthe AGC of a recorder. The recorders used in the video cassetteduplication facilities are specially modified to operate withoutdepending upon this AGC action and can thus record the copy protectedsignal. The Colorstripe™ system depends upon the color time baserecording system of a video cassette recorder. It is not economicallypossible to modify the duplicating video cassette recorders to record asignal with the teachings of the '216 patent. Thus the Colorstripe™system is used primarily in transmission systems; on the output of DVDrecorders and playback machines; and on the output of DVCR machines. Afuller discussion on how the Colorstripe™ system is incorporated inthese systems is discussed below.

Color video signals (both in the NTSC and PAL TV systems) include whatis called a color burst. The color stripe system modifies the colorburst. The suppression of the color subcarrier signal at the TVtransmitter requires that the color TV receiver include an oscillator(in NTSC a 3.58 MHz oscillator) (in PAL a 4.43 MHz oscillator) which isused during demodulation to reinsert the continuous color subcarriersignal and restore the color signal to its original form. Both thefrequency and phase of this reinserted subcarrier signal are criticalfor color reproduction. Therefore, it is necessary to synchronize thecolor TV receiver's local 3.58 MHz or 4.43 MHz oscillator so that itsfrequency and phase are in step with the subcarrier signal at thetransmitter.

This synchronization is accomplished by transmitting a small sample ofthe transmitter's 3.58 MHz or 4.43 MHz subcarrier signal during the backporch interval of the horizontal blanking pulse. FIG. 1A shows onehorizontal blanking interval for an NTSC color TV signal. FIGS. 1B and1C show the details the color burst on two lines of the video signal.The phase of the color burst on successive lines in the NTSC are 180degrees out of phase with each other. The horizontal sync pulse, thefront porch and blanking interval duration are essentially the same asthat for black and white TV. However, during color TV transmission (bothbroadcast and cable) 8 to 10 cycles of the 3.58 MHz (in NTSC) subcarrierthat is to be used as the color sync signal are superimposed on the backporch. This color sync signal is referred to as the “color burst” or“burst”. The color burst peak-to-peak amplitude (40 IRE for NTSC TV asshown) is generally the same amplitude as the horizontal sync pulse.

FIG. 1B shows an expanded view of a part of the waveform of FIG. 1Aincluding the actual color burst cycles. During the color TV blankingintervals, such a color burst is transmitted following each horizontalsync pulse. Similar characteristics for the horizontal blanking intervaland color burst are present in a PAL signal. The differences between PALand NTSC are discussed more fully below.

The phase relationship of the color burst and the color components of anNTSC signal are shown in FIG. 1D. The NTSC color system operates on aquadrature modulation system based upon an R-Y and B-Y or an I and Qsystem. For ease of discussion, we will discuss the R-Y and B-Y system.As can be seen on FIG. 1D the R-Y axis is the vertical axis and the B-Yaxis is the horizontal axis. The Color Burst signal has been specifiedto be on the B-Y axis and is at the 180 degree point relative to a 0degree point as shown on FIG. 1D. The color modulation demodulationprocess depends upon this phase relationship between the various colorcomponents shown in the vector diagram of FIG. 1D and the referencesubcarrier represented by the color burst signal. The color stripeprocesses described in the '216 patent and the material below representa modification of this phase relationship that creates a copy protectedsignal that has an effectiveness to produce a recording of the signalthat has lost its entertainment value while the copy protected signal isdisplayed without artifacts by a TV receiver or monitor (playability).

The phase relationship of the color burst and the color of an unmodifiedPAL signal are shown in FIG. 2C.

The PAL color system like its NTSC counterpart operates on a quadraturemodulation system based upon an U axis and V axis. As can be seen onFIG. 2C the V axis is the vertical axis and the V axis is the horizontalaxis. One of the key differences between the NTSC color system and thePAL TV system is the vector location of the color burst. The PAL ColorBurst signal has been specified to be at +/−45 degrees from the −U Axisrelative to a 0 degree point as shown on FIG. 2C. On an alternating linebasis the V signal switches 180 degrees in phase. The color burst ofeach of these switches in synchronization. On the lines with a +Vsignal, the color burst is at +45 degrees relative to the U axis. On thelines with a −V signal, the color burst is at −45 degrees relative tothe U axis. The color modulation demodulation process depends upon thisphase relationship between the various color components shown in thevector diagram of FIG. 2C and the reference subcarrier represented bythe color burst signal. The so called swinging burst is used to generatea PAL ID pulse within the demodulation process to appropriately switchthe demodulation process to respond to the line by line change in the Vportion of the signal. Due to the unique characteristics of the PAL TVsignal there is a need for an improvement on the color stripe processesdescribed in the '216 patent to improve to create a copy protectedsignal that has an effectiveness to produce a recording of the signalthat has lost its entertainment value while the copy protected signaland to improved the display of the signal without artifacts by a TVreceiver or monitor. For further details on the PAL Color TV system see“Color Television” by Geoffrey Hutson, Peter Shepherd, and James Brice,published by McGraw Hill Book Company,(UK) Limited, Maidenhead,Berkshire, England.

In the embodiments of the color stripe process, no color burst phase(stripe) modification appears in the video lines that have a color burstsignal during the vertical blanking interval. These are lines 10 to 21in an NTSC signal and corresponding lines in a PAL signal. The purposeof keeping these lines modified is to improve the playability of themodified signal. Since these lines are not visible on the playback of arecording there is no improved effectiveness to be achieved by modifyingthese lines. The previous commercial embodiments of the color stripemodifications (modulation of the color burst phase) have occurred inbands of four to five video lines of the viewable TV field followed bybands of eight to ten video lines without the color stripe modulation.The location of the bands is fixed (“stationary”) field-to-field. Thiscolor stripe process has been found to be quite effective for cabletelevision, especially when combined with the teachings of the '603patent discussed above.

In NTSC TV, the start of color burst is defined by the zero-crossing(positive or negative slope) that precedes the first half cycle ofsubcarrier (color burst) that is 50% or greater of the color burstamplitude. It is to be understood that the color stripe process shiftsthe phase of the color burst cycles relative to their nominal (correct)position which is shown in FIG. 1B. The phase shifted color burst isshown in FIG. 1D. The amount of phase shift shown in FIG. 1C may be asgreat as 180° (the maximum possible).

Further, the amount of phase shift in the color stripe process can varyfrom e.g. 20° to 180°; the more phase shift, the greater the visualeffect in terms of color shift. In a color stripe process for PAL TV, asomewhat greater phase shift (e.g. 40° to 180°) is used to be effective.

In any copy protection system there is a need for a proper balancebetween the effectiveness of the copy protected signal in the making ofa deteriorated copy versus the need for no visible effects on theplayability of the copy protected signal. However, certain televisionsets may produce slight playability problems when displaying a signalwith embodiments of the '216 patent. In particular, the visibility ofthe color stripe on a television receiver has been found to beparticularly noticeable in certain “picture in picture”(“p-i-p”)portions of the TV display. These systems use analog to digitalconversion and digital to analog conversion techniques to accomplish the“p-i-p” feature that may be sensitive to the phase errors of the '216embodiment. Therefore, it is an object of this invention to provide animproved method and apparatus for modifying a color video signal so thata conventional television receiver produces a normal color pictureincluding the picture in picture portion from the modified signal,whereas a videotape recording made from the modified signal exhibitsannoying color interference, thus discouraging or inhibiting videotapingof the signal.

Other variations of the Colorstriper™ process are also possible.

SUMMARY

The present invention is directed to a method and apparatus thatsatisfies the need for an for an improved method and apparatus formodifying a color video signal so that a conventional televisionreceiver produces a normal color picture including the picture inpicture portion from the modified signal, whereas a videotape recordingmade from the modified signal exhibits annoying color interference, thusdiscouraging or inhibiting videotaping of the signal.

The present inventors have determined that improvements are possible onthe teachings of above mentioned U.S. Pat. No. 4,577,216, especiallypertaining to playability of the signal on a television receiver ormonitor.

In a first embodiment, it has been found that it is not necessary tocompletely modify a color burst. With typical commercially availabletelevision sets and VCRs, modifying or modulating only part of some ofthe color bursts has been found effective in making a copy protectedsignal while improving the playability on television receivers andmonitors.

A second embodiment improves the playability of the modified signal byextending the color burst signal forward into the so called breezewayportion of the television signal.

A third embodiment additionally improves the playability by extendingthe burst signal beyond the normal end point to just prior to activevideo. With both the second and third embodiments, various combinationsof modified or modulated burst signal with unmodified or unmodulatedburst signal are used to optimize the effectiveness of the copyprotection and the playability of the modified signal.

Within the NTSC color system each of the first three embodiments, thephase of the modified versions is generally 180 degrees from the nominalburst position. Other phase angles are also usable. These threeembodiments are useful in the PAL color system as well.

However, some specialized embodiments are described that take advantageof the differences in the PAL system from the NTSC system. In the PALembodiments, the modified lines comprise a phase shift of either +90degrees relative to the burst phase angle of a normal line or −90degrees relative to the burst phase of the burst phase of a normal line.The differences between various PAL embodiments is the sequence of linemodifications.

It is to be understood that in each of these embodiments it has beenfound that it is not necessary to modify or modulate all of a particularcolor stripe burst.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims and accompanying drawings where:

FIGS. 1A through 1C show standard NTSC TV waveforms;

FIG. 1D shows a vector diagram of an unmodified NTSC signal;

FIG. 2A shows a standard PAL TV waveform;

FIGS. 2B and 2C show a vector diagram of an unmodified PAL signal;

FIGS. 3A to 3E show waveforms illustrating various versions of a firstembodiment of the color stripe process in accordance with the invention;

FIGS. 4A to 4B show waveforms illustrating various versions of a secondembodiment of the color stripe process in accordance with the invention;

FIGS. 5A to 5E show waveforms illustrating various versions of a thirdembodiment of the color stripe process in accordance with the invention;

FIGS. 6A through 6C show waveforms of an embodiment using the splitburst concept without any modified burst;

FIG. 7 shows an exemplary embodiment that combines the embodimentdescribed in FIGS. 3A through 3C, FIGS. 4A through 4B and FIGS. 5Athrough 5C;

FIGS. 8A to 8D show vector diagrams illustrating a first PAL embodimentof the color stripe process in accordance with the invention;

FIG. 9 shows a series of vector diagrams illustrating a second PALembodiment of the color stripe process in accordance with the invention;

FIG. 10 shows a waveform of an exemplary embodiment of a PAL version ofthe invention;

FIG. 11 shows a waveform illustrating various versions of a fourth PALembodiment of the color stripe process in accordance with the invention;and

FIG. 12 shows waveforms illustrating a swinging burst embodiment of thecolor stripe process in accordance with the invention; and

FIGS. 13A and 13B show block diagrams illustrating a general andexemplary apparatus covering the various embodiments of the color stripeprocess in accordance with the invention.

DETAILED DESCRIPTION

The following describes a number of embodiments for an improved methodand apparatus for modifying a color video signal so that a conventionaltelevision receiver produces a normal color picture including thepicture in picture portion from the modified signal, whereas a videotaperecording made from the modified signal exhibits annoying colorinterference, thus discouraging or inhibiting videotaping of the signal.

First is a description relating to waveforms and methods. Second is adescription of various related circuits.

Method Description

The following are various color stripe methods in accordance with theinvention.

A key inventive concept in each of the embodiments described is that ithas been found that it is not necessary to modify or modulate all of aparticular color stripe burst. It has been found that modifying ormodulating only a portion of a color stripe burst is still effective asa copy protection signal for a typical VCR. Also, it has been found thatreducing the portion of the burst that is modified or modulated improvesthe playability of the copy protected signal on television receivers andmonitors. This modification or modulation of only a portion of aspecific color burst signal is colloquially called a split color burstsignal. Variations of this split color burst concept comprise thevarious embodiments described below.

FIGS. 3A through 3G show various versions of a split color burst signalthat are contained within the standard position of a color burst signal.This standard position of a color burst signal is shown in FIG. 1D (forNTSC) and FIGS. 2B and 2C (for PAL).

FIG. 3A shows a color burst with a full burst modification or modulation(the hatching denotes a modified burst signal). FIG. 3C shows a colorburst signal with a approximately. half of the first portion of thenormal burst duration unmodified and the remaining portion of the normalcolor burst duration having a modified or modulated burst phase as shownby the hatching. The amount of phase modification may as little as 20degrees from normal phase to a maximum of 180 degrees from normal phase.

This replacement may be of only a portion of a particular color burst.For instance, of the standard eight to ten cycles of NTSC color burst,one may replace e.g. the first five cycles, the last five cycles, or anyother group of e.g. four to six cycles. The replaced cycles need not beconsecutive; one may replace alternate cycles, leaving “good”(corrected) cycles interspersed with “bad” (color stripe) cycles. Italso is possible to add corrected color burst cycles outside of theirnormal location and overlying the horizontal sync pulses, since thesewill be detected by a VCR. It is to be understood that the recognitionby the present inventors that only a portion of a particular color burstneed be replaced forms a part of the invention. Moreover, the partialreplacement is also applicable to other of the embodiments describedhereinafter.

FIG. 3B shows a version of split color burst where the modified portionis within a first portion of the normal color burst duration and theunmodified portion is in the later portion of the normal burst duration.

FIGS. 3D and 3E show where the unmodified color burst and modified colorburst portions are positioned in a sandwich manner within the normalcolor burst duration. FIG. 3E shows the unmodified portions to be on theends of the normal burst duration with the modified portion being in themiddle. The amount of modified portions versus the unmodified portion isadjusted for an optimum balance between effectiveness and playability asdiscussed above.

FIG. 3D shows where the unmodified color burst and modified color burstportions are positioned in a another sandwich manner within the normalcolor burst duration. FIG. 3D shows the modified or modulated portionsto be on the ends of the normal burst duration with the unmodifiedportion being in the middle. The amount of modified or modulatedportions versus the unmodified or unmodulated portion is adjusted for anoptimum balance between effectiveness and playability as discussedabove.

FIGS. 4A and 4B show embodiments of a version of the color stripeprocess colloquially called advance split burst. In these versions itwas determined that playability was improved by advancing the areawithin the back porch where the color burst (modified or unmodified)would exist.

FIG. 4A shows a basic combination of the advanced concept with a splitcolor burst. In this particular version the burst envelope is extendedforward to the trailing edge of horizontal sync. As shown in FIG. 4A,the color burst comprises a modified or modulated color burst from thetrailing edge of sync through and into a portion of the normal burstduration. The remainder of the normal burst duration has an unmodifiedburst portion.

FIG. 4B shows another version of the advanced split color burst. Herethe color burst envelope begins during the horizontal sync duration andcontinues into the normal color burst duration. As in the previousversion of the advanced split color burst, the remaining color burstsignal within the normal color burst duration is an unmodified colorburst.

One of the advantages of having the advanced split color burst in theNTSC system is that the detection area of the color burst signal in aVCR tends to be closer to the trailing edge of horizontal sync than doesthe detection area of the color burst in a television receiver ormonitor. Thereby, in the NTSC system with an advanced split color burst,the VCR tends to lock onto a modified signal and the television receivertends to lock onto an unmodified signal.

FIGS. 4A and 4B show the advanced split color burst system with theunmodified or unmodulated version in the first portion of the advancedcolor burst. It should be understood as will be shown later that acombination of the advanced split color burst could use the “sandwich”approach discussed above is another possible variation of the colorstripe system.

FIGS. 5A through 5E show another embodiment of the split color burstsystem. As shown in FIGS. 5A through 5E there are advantages to havingthe normal burst envelope extended forward to a point that may extend asfar as the front porch area of the horizontal blanking area. It has alsobeen found to be advantageous to extend the normal color burst envelopebeyond the normal burst period towards the active picture area. Thisextension of the normal is limited only by the maximum horizontalblanking area and the start of active video. FIG. 5A shows a normalunmodified color burst. FIG. 5B shows an extended color burst with anindication of the end of normal color burst. The extended period mayhave normal color burst or modified or modulated color burst. FIG. 5Cshows an example of a color burst signal having the earlier portioncontain normal color burst and the later portion including the extendedportion containing modified or modulated color burst. FIG. 5D shows thereverse. The point at which the switching between modified color burstand unmodified color burst occurs is variable and subject toexperimental results for the maximum balance between effectiveness andplayability as discussed above.

FIGS. 6A through 6C show an embodiment of the modification to the colorburst where there is no area of modified burst. However, the concept ofsplit color burst prevails when the width of the normal color burstenvelope is narrowed. In this embodiment, the number of cycles of colorburst is reduced. As shown in FIGS. 6A through 6C the shortened colorburst is varied in its position within the normal color burst window. Onthe lines containing this modification, disturbances to the colorfidelity will occur in a recording of the signal, but the playabilitywithin a TV receiver or monitor is maintained.

Each of the embodiments discussed in FIGS. 3A through 3E, FIGS. 4Athrough 4B, FIGS. 5A through 5E and FIGS. 6A through 6C are applicableto the NTSC color format and the PAL color format.

FIG. 7 shows an NTSC exemplary embodiment that combines the elements ofthe above identified embodiment. The NTSC exemplary embodiment, calledAdvanced Switched Burst (ASB) has the capability of programming variouscombinations of the embodiments described above. The burst envelopecomprises three zones. Zone 1 (burst start) beginning 4.96 μsecs. afterthe leading edge of horizontal sync. Zone 1 ends 1.484 μsecs afternormal burst start. Zone 2 begins and ends at the end of Zone I. In thisparticular embodiment, there is no Zones 2 and 3 per se. begins afterthe Zone II point and extends 1.48 μsecs. to the end of burst.Therefore, this particular embodiment, color burst has a width of 4.96μsecs. The Zone I area will contain modified (inverted 180°) subcarrier.Normal phase subcarrier is used in Zone 2 (zero duration and Zone 3.

As discussed above, the number of lines containing modified or invertedsubcarrier in the color burst area is limited to groups of linesfollowed by larger groups of line not containing modified or invertedsubcarrier in the color burst. The exemplary embodiment discussed aboveis available in two basic versions. One is called the 2 line version andthe second is called the 4 line version. Table 1a shows the exmplaryembodiment of a Colorstripe™ measurements for NTSC. Table 1a.2 showsboth line number configurations. Other combinations are possible. Theexemplary embodiment is the result of experimental work towards findingan optimal mix of playability and effectiveness discussed above.

TABLE 1a Summary of 525/60/NTSC Measurements Measurement Parameter (±S)Burst Normal Start Point 5.3 ±0.15 (Colorstripe Line) Burst AdvancedStart Point 4.96 ±0.15 (Colorstripe Line) (Note 1) Envelope Rise Time10%-90% 0.3 +0.1/−0.2 Burst Start to First Phase 1.48 ±0.07 Switch PointFirst to second phase switch 0 points Second Phase Switch Point to end1.48 ±0.15 of burst (Note 1) Envelope Fall Time 10%-90% 0.3 +0.1/−0.2

Note 1: Start and End points must be such that total burst duration forthe default configuration is 2.96+0.15/−0.07

TABLE 1b LINE NUMBERS INCORPORATING ADVANCED SPLIT BURST WAVEFORM (NTSC)Advanced Split Burst Advanced split Burst 4-Line version 2-Line version(21-Line Spacing) (17-Line Spacing First line in stripe First line instripe Stripe No. Field 1 Field 2 Field 1 Field 2 1 24 297 30 301 2 45318 47 318 3 66 339 64 335 4 87 360 81 352 5 108 381 98 369 6 129 402115 386 7 150 423 132 403 8 171 444 149 420 9 192 465 166 437 10 213 486183 454 11 234 507 200 471 12 217 488 13 234 505

As discussed above, these embodiments are applicable to the NTSC systemas well as the PAL system. However, since the PAL uses the color burstin a slightly different way from NTSC, four embodiments of PAL onlycolor stripe systems are described below.

The standard PAL color signal has several significant differences fromthe standard NTSC signal. Some of these differences are related to thescanning standard used. These scanning differences create the need fordifferent subcarrier frequency. However, the most significant differenceis the use of the swinging burst and the alternating phase relationshipsbetween adjacent lines within a field. FIG. 2A shows one horizontalblanking interval for an PAL color TV signal. FIGS. 2B and FIG. 2C showthe vector display of a color bar signal color burst details in a PALsystem. One skilled in the art would fully understand that there is a180 degree change in the V component of every color component on a lineby line basis. Additionally as can be seen from FIG. 2C there is acorresponding phase change in the color burst signal on a line to linebasis. The color burst component and color components that occur whenthe burst is the +45 degree point relative to the U Axis are the socalled NTSC lines. The color burst component and color components thatoccur when the burst is the −45 degree point relative to the U Axis arethe so called PAL lines.

In the NTSC system the phase of the color burst is 180 degrees to thecolor signals 0 degree phase reference. For a PAL signal, however, thecolor burst also has to identify the V portion of the subcarrier phasewhich is switched during transmission by 180 degrees on alternate lines.The burst phase is therefore also switched on alternate lines and is at135 degrees on NTSC lines and 225 degrees on PAL lines. The PAL lineidentification at the receiver may then be achieved by the phasedetection of the 180+/−45 degree switched or swinging burst. As can beseen in FIG. 2B the chroma signal switches about the U Axis such thatfor example a blue signal appears at approximately 350° relative to 0°on the line when color burst is at 135°. A blue signal is atapproximately 10° relative to 0° on the line when the color burst is at225°.

One embodiment of the invention utilizes the four line color stripegroup as discussed above. In an unmodified signal, the first line ofsuch a four line group would have a so-called NTSC burst angle of 135degrees as shown in FIG. 8A. The second line of the four line groupwould be the so-called OPAL burst angle of 225 degrees as shown in FIG.8B. The same pattern repeats in the third and fourth lines of the fourline pattern. The remaining lines follow the same normal pattern.

However, the embodiment of the invention has the phase angles in thefour line pattern modified as shown by dotted lines in FIGS. 8A through8D. The so-called NTSC burst angle of line 1 and 3 moved 90 degrees toan angle of 45 degrees. The so called PAL burst angle of lines 3 and 4are moved 90 degrees to 315 degrees. The invention is not limited to afour line sequence. It is possible that a 2, 4, 6, 8, or more linesequence will be effective.

The advantage of this copy protection method is that the so called PALID pulse pattern generated by the +/−45 degree from the U axis isunchanged. The television receiver is not affected by the changes of thephase angles relative to the V axis as shown in FIGS. 8A through 8D.However, the color time base processing in a recording VCR is disturbedby such a variation from the standard signal. Variations of thisembodiment may include phase angle changes other than 90 degrees, solong as the PAL ID pulse is not disturbed.

Another embodiment as shown in the vector diagrams in FIG. 9 has a oneline modification of the color burst signal in between lines having thenormal color burst signal. It has been found through experimentaltesting that the playability of the modified signal may be improved byusing variations of a one line version of the signal modification. As anexample in a five line portion of a field, the first line may be amodified NTSC line, followed by an unmodified PAL line in turn followedby a modified NTSC line, followed by an unmodified PAL

This five line sequence is shown in the last five vector diagrams ofFIG. 9, sequence could also have modified PAL lines with unmodified NTSClines. The five line sequence can also be a lower number of lines or agreater number of lines. It has been found experimentally that there isa need for approximately 34 line groups of unmodified lines for TVmonitor playability purposes.

The advantage of this copy protection method is that the so called PALID pulse pattern generated by the +/−45 degree from the U axis isunchanged. The television receiver is not affected by the changes of thephase angles relative to the V axis as shown in FIGS. 8A-8D. However,the color time base processing in a recording VCR causes color phaseerrors by such a variation from the standard signal. Variations of thisembodiment may include phase angle changes other than 90 degrees, solong as the PAL ID pulse is not disturbed.

Table 2a and FIG. 10 show an exemplary embodiment of color stripemeasurements for PAL. Table 2b shows both line number configurations. InTable 2a, the line numbers indicate the first line of a two or threeline sequence. In the two line sequence, there are two lines containingmodified color burst followed by 32 lines of unmodified color burst. Inthe three line sequence, there are three lines containing modified colorburst followed by 31 lines of unmodified color burst. Other combinationsare possible. The exemplary embodiment is the result of experimentalwork towards finding an optimal mix of playability and effectivenessdiscussed above.

TABLE 2a Summary of 625/50/PAL Measurements Measurement Parameter (±S)Burst Normal Start Point 5.6 ±0.15 (Colorstripe Line) (Note 1) BurstAdvanced Start Point 4.96 ±0.15 (Colorstripe Line) Envelope Rise Time10%-90% 0.3 +0.1/−0.2 Burst Start to First Phase 1.185 ±0.07 SwitchPoint First to second phase switch 0 points Second Phase Switch Point toend 1.185 ±0.15 of burst (Note 1) Envelope Fall Time 10%-90% 0.3+0.1/−0.2

Note 1: Start and End points must be such that total burst duration forthe default configuration is 2.25+0.15/−0.07

TABLE 2b LINE NUMBERS INCORPORATING COLORSTRIPE BURST WAVEFORM (PAL)Colorstripe Burst 2 or 3-Line version (34-Line Spacing) First line instripe Stripe No. Even Field Odd Field 1 27 356 2 61 390 3 95 424 4 129458 5 163 492 6 197 526 7 231 560 8 265 594

NOTES:

1. This table uses the CCIR 625/50/PAL line numbering convention.Subtract 313 from Odd Field line numbers above to obtain line numbers in“Odd Field/L1” to “Odd Field/L312” format.

2. The line numbers listed in the table are the first line of a 2 or 3line sequence as appropriate.

3. The above configurations are within Rev 6.1 programming range.

FIG. 11 shows another embodiment for a PAL color stripe system. Thisembodiment includes the spilt-burst concept with the modified portion inthe later portion of a normal color burst envelope. The phase of themodified area is at 0° or at the −U relative to the average position ofthe normal PAL burst phase signals. In the earlier embodiment, themodified phase angle did not disturb the so called PAL ID pulse in themodified area. In this embodiment, the PAL pulse is maintained in theunmodified portion, whereas the color subcarrier phase is disturbed bythe modified color burst having a phase angle 180° away (opposite) fromthe average value of the swinging burst. This embodiment is an effectivecopy protection system.

FIG. 12 shows another embodiment for a PAL color stripe system. Thisembodiment includes the split-burst concept with the modified portion inthe later portion of a normal color burst envelope. The phase angle ofthe unmodified area is the normal swinging burst angle for theparticular line. The modified portion has a phase angle set to be 180°from the swinging burst angle [A or B] of the opposite swinging burstangle [(B) or (A)]. For example in line 1 as shown on FIG. 11, theunmodified burst area has the normal swinging burst angle, (135°) andthe modified burst area has an angle of 45° (180° from the 225° angle ofthe opposite line's swinging burst). In line 2 of the sequence, theunmodified burst is at its normal 225° angle. The modified portion has aburst phase angle of 335° (180° from the 135° angle of the oppositeline's swinging burst).

In the earlier embodiments, the modified phase angle did not disturb theso called PAL ID pulse in the modified area. In this embodiment, the PALpulse is maintained in the unmodified portion, whereas the colorsubcarrier phase is disturbed by the modified color burst having a phaseangle 180° away from the average value of the swinging burst. Thisembodiment is an effective copy protection system.

In each of the embodiments described above that involve an advanced orextended color burst envelope, the lines with normal burst signalsthroughout the burst envelope have a normal burst width. However, thisdisclosure is not limited to that condition. There may be conditionswhereby all lines with a color burst signal will contain advanced andextended burst envelopes whether the burst has any phase modification ornot.

An additional embodiment is to modify the horizontal sync width and/orposition. One example would be to narrow the sync width by 1 to 2 μsecs.and fill the extended blanking area with extended burst. Yet anotherexample is to widen the horizontal sync by 1 to 2 μsecs. and fill theextended horizontal sync with extended burst. Another variation is tomove the leading edge of horizontal sync 1-2 μsecs. and then theextended back porch with the modified color burst. Each of theseadditional embodiments are designed to improve the playability with aminimum of effect on the effectiveness of the copy protection.

Digital video tape recorders and digital play back devices are nowbecoming commercially available for consumer use. To maintaincompatibility with analog video broadcast signals and analog video taperecorders, these consumer digital video tape recorders and digitalplayback devices will be “hybrid” digital and analog systems. Suchsystems will have the capabilities of current analog video cassetterecorders to record and playback analog signals, while still havingequivalent digital capabilities. Thus these new hybrid digital taperecorders will have the capability internally to convert input analogsignals into digital signals, and record the digital signals as adigital data stream on the tape or disc. During playback the digitaldata stream from the tape or disc will be available both as a digitalsignal for display by a digital television set (not currently available)or be reconverted within a hybrid video tape or tape recorder or to aconventional analog video signal (such as the NTSC signal used in theUnited States.) The capability of the system internally to convert thereceived analog signals to a digital data stream will be importantbecause currently there are no sources (either tape or broadcast) ofdigital video program material available to consumers.

Such hybrid video recorders employ a “consumer” digital recording formatdiffering from the standards of present professional digital systems.Such digital video recorder will likely include a conventional “frontend” RF tuner and also an RF modulator on the output side, as do presentconventional analog VCRs. (By analog video here is meant NTSC, PAL,SECAM or YC.) The digital recording standard for consumers isessentially a data structure that represents the video signal as astream of (binary) data bits along with suitable error concealmentencoding, together with a physical tape standard.

Problems Posed by Digital Recording

Since digital video tape or disc recorders and digital playback deviceswill be capable of high fidelity reproduction which in turn willencourage copying, it is important that such recorders for consumer usebe designed to inhibit or discourage unauthorized recording. Forinstance it is important to prevent use of recorders for illegallyduplicating copy-righted video material, and also to prevent playingback of such illegally duplicated material. Currently available analogvideo copy protection techniques are not useful in the digital domain.Hence there is a need for a new copy protection system suitable for usewith such hybrid digital and analog video tape recorders, where thematerial recorded on the tape is a digital data stream. A typicalsituation to be prevented is use of a hybrid video tape recorder to copyan output signal from a conventional VHS VCR, where the tape played backfrom the VHS VCR has a conventional copy protection process applied toit. The problem is to prevent the new hybrid digital-analog video taperecorder from copying the material from such a tape. Otherwise, theexistence of such hybrid recorders would encourage copyrightinfringement.

A hybrid digital video recording system is described in U.S. Pat. No.5,315,448 by Ryan issued on May 24, 1994 (incorporated by reference).

Integrated Circuit Implementation

A first apparatus embodiment comprises imbedding the color stripetechnology along with other copy protection technology into anintegrated circuit. The other copy protection technology comprises thetechnology described in U.S. Pat. Nos. 4,631,603 and 4,819,098 issued toRyan on Dec. 23, 1986 and Apr. 4, 1989 respectively (incorporated byreference). Generally the integrated circuit includes a digital toanalog converter to convert the digital video stream to an analog videostream which is encoded into an NTSC, PAL or YC format. The copyprotection technology is added in the encoder stage and combined withthe encoded output. The technology used in the integrated circuits isusually of the ASIC variety using multitudes of gates to produce thedesired copy protection output waveform.

Three specific applications for such an integrated circuit incorporatingthe copy protection technology are the Digital Video Disc Players andRecorders, digital video cassette players and recorders and digitalset-top boxes used in the cable industry and satellite to home industry.These specific applications include a programability of the integratedcircuit permitting a change of the waveform parameters. In the case of atransmission system, the bits to change the default values of thewaveform are transmitted with the signal. In the case of a DVDPlayer/Recorder and digital video cassette player/recorder the bits areincluded within the disc or cassette tape. FIG. 13A is a general blockdiagram of such an integrated circuit implementing the embodiments ofthe invention and the teachings of the '603 patent.

General Circuit

A second apparatus embodiment implementing the various embodimentsdescribed above is shown FIG. 13B. Generally an apparatus to produce thevarious color stripe embodiments described above comprises: 1) aSubcarrier Processor, 2) a Burst Gate Generator and 3) a Line Generator.

FIG. 13A illustrates an exemplary circuit to produce a color stripesignal of the various embodiments described above.

A Copy Protection Apparatus 50 has an unmodified Video Input Signal 52.This signal may be a NTSC or PAL analog signal or a digital data streamrepresenting a video signal to be copy protected. The input signal isinputted to a Copy Protection Inserter 60, a Subcarrier Processor 54, aBurst Gate Generator 56, and a Line Selector 58. The SubcarrierProcessor 54 detects the color burst signal within Video Input Signal 52and generates a 3.58 MHz. or a 4.43 MHz. subcarrier (depending onwhether it is processing an NTSC or a PAL signal).

The Burst Gate Generator 56 is programmed to generate the appropriategating signals for the Copy Protection Inserter 60 to instruct the CopyProtection Inserter to insert a normal phase subcarrier or a modifiedphase subcarrier.

The Line Selector 58 is programmed to instruct the Burst Gate Generator56 and the Copy Protection Inserter which lines are to produce amodified burst and which line are to reproduce the burst signal presenton the Video Input Signal 52. Apparatus 50 may be combined with theappropriate circuitry to produce the pseudo-sync AGC pulse pairs taughtin the '603 patent.

Exemplary Circuit

FIG. 13B is illustrative of an apparatus to implement the variousembodiments discussed above. An improved color stripe system isimplemented within the various elements of system 10. Each elementwithin system performs functions well known to one skilled in the art ofvideo engineering. A composite video signal 11 is inputted to InputAmplifier 12. Amplifier 12 sets the level of the video signal to anappropriate level for the remaining elements of the color stripe system.

A first output of Input Amplifier 12 is coupled to Sync Separator 14.Sync Separator 14 removes the horizontal and vertical synchronizingsignals from the composite video for further use in improved colorstripe system. Outputs of Sync Separator 14 are coupled to inputs ofBurst Gate Generator 16 and Line Counter 18. Burst Gate Generator 16uses the horizontal and vertical synchronizing pulses from SyncSeparator 14 to produce a burst gate signal. In the NTSC format, thenormal burst gate signal would begin approximately 5.3 microsecondsafter the leading edge of horizontal sync and end after the equivalentof 9 cycles of subcarrier (2.52 microseconds). Burst Gate Generator 16is programmed to produce a widened burst gate on those lines where anadvanced and/or extended burst gate is desired. Line Counter 18 uses thehorizontal and vertical synchronizing pulses from Sync Separator 14 andis programmed to determine which lines will contain the color stripeinformation. An output of the Line Counter 18 is coupled to Burst GateGenerator 16 to instruct Burst Gate Generator 16 which lines require awidened burst gate. In one embodiment the ratio of lines having thecolor stripe signal to those not having the color stripe signal is{fraction (4/16)}. That is four lines out of twenty in each field havethe color stripe signal. Additionally, the line count is arranged sothat comparable lines in each field contain the color stripe signal.This pairing up of the color stripe portions increases the visibility ofthe color stripe in the playback of the recorded signal.

A first output of Burst Gate Generator 16 is coupled to an InversionGate 20. Which determines which portions of the color burst signal willcontain phase inverted color burst. Modification Gate 20 may beprogrammed to provide for inverted color burst phase in one or moreparts of the color burst signal as shown in the various embodimentsabove.

A second output of Input Amplifier 12 is coupled to Chroma Separator 24.The output of Chroma Separator 24 comprises the chroma information andhigh frequency luminance information within the video signal. Sincethere is no luminance information during the color burst portion, thereis only chroma information during the color burst portion of the outputof Chroma Separator 24. The output of Chroma Separator 24 is coupled toa Burst Separator 26. Burst Separator 26 also has a burst gate inputfrom the Burst Gate Generator 16.

The output of Burst Separator 26 contains only the color burst signalretrieved from Input Signal 11 via Chroma Separator 24 and BurstSeparator 26.

The color burst signal from Burst Separator 26 is coupled to SubcarrierOscillator 40 to produce a subcarrier signal synchronous with theincoming burst signal (3.58 MHz. in NTSC and 4.43 MHz. in PAL). Anoutput of Subcarrier Oscillator 40 is coupled to Burst Generator 42.Burst Generator 42 also receives a Burst Gate Signal from Burst GateGenerator 16. The width of the burst signal generated by Burst Generator42 is determined by the Burst Gate Generator. This may be varied by thecombination of burst gates on lines having no modification being of onewidth and the lines with burst modification having a different width.These variation are determined by a combination of the Burst GateGenerator 16 and Line Counter 18.

The output of Burst Generator 42 is coupled to a Phase Shifter 28 and tothe first input of Switch 30. In the NTSC system, the phase modificationis generally 180°. In the PAL format, the Phase Shifter 28 may have aninput from Line Counter 18 to instruct Phase Shifter 28 to producedifferent phase modifications on different lines as discussed above.Generally the phase modification in PAL is +90° on some lines and −90°on other lines. The output of Phase Shifter 28 is coupled to a secondinput of Switch 30. Inversion Gate 20 and Line Counter 18 are coupled toAnd Gate 22 to produce Control Signal 21. When And Gate 22 produces asignal indicating no burst phase modification requirement, ControlSignal 21 places Switch 30 in a position to pass normal color burst.When And Gate 22 produces a signal indicating a need for color burstphase modification, Control Signal 21 places Switch 30 to pass invertedcolor burst. The output of Switch 30 may be coupled to a first input ofBurst Inserter 34. However, the output preferably is supplied to theburst inserter 34 via a burst envelope shaper 38, as described below.

A third output of Input Amplifier 12 containing the processed inputsignal is coupled to an input of Burst Blanker 32. Another output ofBurst Gate Generator 16 is coupled to Burst Blanker 32. Burst Blanker 32blanks out all color burst information from Video Signal 13 using theburst gate signal from Burst Gate Generator 16. The output of BurstBlanker 32 containing Video Signal 15 is inputted to a second input ofBurst Inserter 34. As discussed above Video Signal 15 has no color burstinformation. The output of Switch 30 contains the color stripe colorburst generated by a combination of elements 24, 26, 28, 12, 14, 16, 18,20, 22 and 30.

It has been determined in experimental testing that the effectivenessand playability of the modified signal are affected by shape of thecolor burst waveform. Therefore, the output of Switch 30 is coupled tothe Burst Envelope Shaper 38 of previous mention that controls the riseand fall time of the color burst waveform. The output of Burst EnvelopeShaper is then coupled to Burst Inserter 34 Burst Inserter 34 insertsthe color stripe color burst with the Video Signal 15 which contains nocolor burst information to produce a composite video signal containingthe improved color stripe color burst and its related composite videoinformation.

The output of Burst Inserter 34 is coupled to Output Amplifier 36.Output Amplifier 36 provides the appropriate signal processing toproduce a composite video signal with the correct levels and outputimpedance for use in a video system.

This disclosure is illustrative and not limiting. Further modificationswill be apparent to one skilled in the art and are intended to fallwithin the scope of the appended claims.

We claim:
 1. A method of improving the playability of a copy protectedoriginal video signal, the copy protected original video signalincluding a plurality of video lines with selected video lines includinga color stripe burst having a predetermined duration and a selectedphase other than a normal color burst phase, the method comprising:determining the duration of the color stripe burst in the selected videolines of the original video signal; and modifying a phase of a selectedportion or portions of said duration of the color stripe burst in chosenlines of the selected lines to be the phase of the normal color burst,whereby the playability of the copy protected original video signal isimproved.
 2. The method of claim 1, wherein the modifying includesshifting the selected phase of She portion or portions of the colorstripe burst by 180°.
 3. The method of claim 1, wherein the selectedphase of the color stripe burst is from about 20° to 180°.
 4. The methodof claim 1, wherein up to 60% of the duration of the color stripe burstis modified.
 5. The method of claim 1, wherein a duration of the colorstripe burst is eight to ten cycles of a color subcarrier signal, andthe act of modifying includes modifying up to four to six of the cycles.6. The method of claim 1, wherein in each video field at least one bandof video lines is subject to the modifying of the portion or portions ofthe color stripe burst, followed by a band of video lines which are notsubject to the modifying of the portion or portions of the color stripeburst.
 7. The method of claim 1, wherein a normal color burst phaseportion precedes a selected phase portion of the color stripe burst. 8.The method of claim 1, wherein a selected phase portion precedes anormal color burst phase portion of the color stripe burst.
 9. Themethod of claim 1, wherein a first selected phase portion precedes anormal color burst phase portion and a second selected phase portionfollows the normal color burst phase portion.
 10. The method of claim 1,wherein a first normal color burst phase portion precedes the selectedphase portion and a second normal color burst phase portion follows theselected phase portion of the color stripe burst.
 11. The method ofclaim 1, wherein the original video signal is an original NTSC videosignal.
 12. The method of claim 1, where the original video signal is anoriginal PAL video signal.
 13. The method of claim 1 wherein a videoline includes a horizontal sync signal, further including: modifying thehorizontal sync signal position and/or width.
 14. The method of claim 1including: reducing the amplitude of a selected portion of the colorstripe burst.
 15. A method of improving the playability of a copyprotected original video signal, the copy protected original videosignal including a plurality of video lines with selected video linesincluding a color stripe burst having a predetermined duration and aselected phase other than a normal color burst phase, the methodcomprising: increasing the duration of the color stripe burst in theselected lines of the copy protected original video signal; andmodifying a phase of one or more portions of the extended duration ofthe color stripe burst to be other than the selected phase, whereby theplayability of the copy protected original video signal is improved. 16.The method of claim 15, wherein increasing the duration of the colorstripe burst comprises beginning the color stripe burst duration beforea normal color burst duration.
 17. The method of claim 15, whereinincreasing a duration of the color stripe burst comprises ending thecolor stripe burst duration after a normal color burst duration.
 18. Themethod of claim 15, wherein increasing a duration of the color stripeburst comprises beginning a color stripe burst duration before a normalcolor burst duration and ending the color stripe burst duration after anormal color burst duration.
 19. The method of claim 15, wherein amodified color stripe burst duration begins at a tailing edge of arespective horizontal sync.
 20. The method of claim 15, wherein amodified color stripe burst duration begins between a leading edge of arespective horizontal sync and a trailing edge of the horizontal sync.21. The method of claim 15, wherein an end of a modified color stripeburst duration is at the beginning of a respective active video line.22. The method of claim 15, wherein the modification of a duration ofthe color stripe burst comprises: increasing the duration of the colorstripe burst by adding a first portion to the color stripe burstduration between the trailing edge of a respective horizontal sync andthe beginning of a duration of a normal color burst; and furtherincreasing the duration of the color stripe burst by adding a secondportion following the duration of the normal color burst that ends priorto the beginning of a respective active video line.
 23. The method ofclaim 22, wherein the phase modification comprises: modifying a phase ofa first portion of the modified color stripe burst duration; andretaining a normal color burst phase in a second portion of the modifiedcolor stripe burst duration.
 24. The method of claim 15, wherein theoriginal video signal is an original NTSC video signal.
 25. The methodof claim 15, where the original video signal is an original PAL videosignal.
 26. The method of claim 15 wherein increasing the durationincluding adding extra cycles of the selected phase other than thenormal color burst phase prior to the existing color stripe burst. 27.The method of claim 15 wherein increasing the duration includes addingcycles of the selected passe other than the normal color burst phase inthe region of the horizontal sync and extending to the existing colorstripe burst.
 28. The method of claim 15 wherein a video line includes ahorizontal sync signal, further including: modifying the horizontal syncsignal position and/or width.
 29. An apparatus for modifying an originalvideo signal so as to improve the playability of the original videosignal, the original video signal including a plurality of video lineswith selected video lines including a color stripe burst having apredetermined duration and a selected phase other than a normal colorburst phase, comprising: a burst gate generator receiving the originalvideo signal for producing a burst gate signal; a copy protectioninsertion device coupled to receive the burst gate signal; a lineselector receiving the original video signal for producing a line countto indicate to the copy protection insertion device which lines of theoriginal video signal are to be modified; a subcarrier processorreceiving the original video signal for modifying a portion(s) of thepredetermined duration of the color stripe burst signals; and a videoinput for also supplying the original video signal to the copyprotection insertion device; wherein the combination of die outputs fromthe subcarrier processor, the burst gate generator and the line selectorare supplied to the copy protection insertion device to modify the videosignal so as produce a copy protection video signal, whereby theplayability of the original video signal is improved.